I am testing the following patch for PR79547. Those builtins do not
return anything that can be used to re-construct the pointer(s) passed
to them.
Queued for GCC 8.
Richard.
2017-02-16 Richard Biener <rguent...@suse.de>
PR tree-optimization/79547
* tree-ssa-structalias.c (find_func_aliases_for_builtin_call):
Handle strlen, strcmp, strncmp, strcasecmp, strncasecmp, memcmp,
bcmp, strspn, strcspn, __builtin_object_size and __builtin_constant_p
without any constraints.
* gcc.dg/tree-ssa/strlen-2.c: New testcase.
Index: gcc/tree-ssa-structalias.c
===================================================================
--- gcc/tree-ssa-structalias.c (revision 245501)
+++ gcc/tree-ssa-structalias.c (working copy)
@@ -4474,6 +4474,22 @@ find_func_aliases_for_builtin_call (stru
process_all_all_constraints (lhsc, rhsc);
}
return true;
+ /* Pure functions that return something not based on any object. */
+ case BUILT_IN_STRLEN:
+ case BUILT_IN_STRCMP:
+ case BUILT_IN_STRNCMP:
+ case BUILT_IN_STRCASECMP:
+ case BUILT_IN_STRNCASECMP:
+ case BUILT_IN_MEMCMP:
+ case BUILT_IN_BCMP:
+ case BUILT_IN_STRSPN:
+ case BUILT_IN_STRCSPN:
+ case BUILT_IN_OBJECT_SIZE:
+ case BUILT_IN_CONSTANT_P:
+ /* We don't need to do anything here. No constraints are necessary
+ for the return value and call handling for pure functions is
+ special-cased in the alias oracle. */
+ return true;
/* Trampolines are special - they set up passing the static
frame. */
case BUILT_IN_INIT_TRAMPOLINE:
Index: gcc/testsuite/gcc.dg/tree-ssa/strlen-2.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/strlen-2.c (nonexistent)
+++ gcc/testsuite/gcc.dg/tree-ssa/strlen-2.c (working copy)
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-strlen" } */
+
+void f (unsigned);
+
+void f3 (void)
+{
+ char s[] = "1234";
+
+ f (__builtin_strlen (s));
+ f (__builtin_strlen (s));
+ f (__builtin_strlen (s));
+}
+
+/* { dg-final { scan-tree-dump-times "strlen" 1 "strlen" } } */
